I have the same problem..it comes on sometimes..nothing happens..I think it's just sensor problems as my brake lights sometimes stay on after I shut it off as well..I am just gonna replace em when I feel like it..no big deal.

I have a '98 Laredo. (only got it 2 months ago).
My ABS light also came on at times. I spoke to the previous owner, and he said it's been doing that for the last 5 years! The dealer replaced the rear sensors twice - no change. They eventually gave up and told him to live with it or sell the car!
This weekend I was determined to find it, so I started from the back working forward with a multi-meter.
Check the connection underneath the rear seat. Two wires each. One black and one red connector. These had a bad connection. To check: Start the car and then handle the wires/connections, you will probably see the light come on. I just opened the connectors and squeezed them a bit closed for a better connection. I did not want to solder them together as I do not know how sensitive the system is.
I hope this works for you.